1. Field of the Invention
The present invention relates to an apparatus to adjust the over-scanning amount of a video scan and a method of controlling the apparatus. In the present invention, over-scanning is adjusted by varying the amount of signal information.
2. Description of the Prior Art
Generally, the actual horizontal size of the video signals which are to be displayed on a screen is larger than the effective size of the picture which is watched by users.
The difference between the horizontal width of the actual video signals and the effective size of the picture is called "over-scanning amount".
The percentage of the over-scanning amount is called "over-scanning rate". When a user selects an over-scanning adjustment function, the over-scanning can be adjusted if a microcomputer judges that the over-scanning rate is too small or too large.
Conventionally, the over-scanning is adjusted by adjusting the magnitude of the horizontal deflections.
FIG. 1 illustrates the conventional over-scanning adjusting method. The relationship of the over-scanning amount to the deflections will be described referring to FIG. 1. If it is assumed that the size of the effective watchable picture is c, and that the magnitude of the horizontal deflection is A, then the over-scanning amount is a-c. If the magnitude of the horizontal deflection is B, then the over-scanning amount is b-c. That is, if the horizontal deflection is increased from A to B, then the over-scanning amount increases as much as b-a.
If the over-scanning amount is too large, then the magnitude of the horizontal deflection is reduced to decrease the over-scanning amount. On the other hand, if the over-scanning amount is too small, then the magnitude of the horizontal deflection is increased to increase the over-scanning amount. In this way, the over-scanning is adjusted.
In this conventional over-scanning amount adjusting method, however, when the deflection is varied, not only is the picture size varied but the brightness and the contrast are also varied. Such unintended changes in the brightness and contrast of the picture cause the viewer to have eye fatigue.